C++ MySQL++ Delete query statement brain killer question - c++

I'm relatively new to the MySQL++ connector in C++, and have an really annoying issue with it already!
I've managed to get stored procedures working, however i'm having issues with the delete statements. I've looked high and low and have found no documentation with examples.
First I thought maybe the code needs to free the query/connection results after calling the stored procedure, but of course MySQL++ doesn't have a free_result method... or does it?
Anyways, here's what I've got:
#include <iostream>
#include <stdio.h>
#include <queue>
#include <deque>
#include <sys/stat.h>
#include <mysql++/mysql++.h>
#include <boost/thread/thread.hpp>
#include "RepositoryQueue.h"
using namespace boost;
using namespace mysqlpp;
class RepositoryChecker
{
private:
bool _isRunning;
Connection _con;
public:
RepositoryChecker()
{
try
{
this->_con = Connection(false);
this->_con.set_option(new MultiStatementsOption(true));
this->_con.set_option(new ReconnectOption(true));
this->_con.connect("**", "***", "***", "***");
this->ChangeRunningState(true);
}
catch(const Exception& e)
{
this->ChangeRunningState(false);
}
}
/**
* Thread method which runs and creates the repositories
*/
void CheckRepositoryQueues()
{
//while(this->IsRunning())
//{
std::queue<RepositoryQueue> queues = this->GetQueue();
if(queues.size() > 0)
{
while(!queues.empty())
{
RepositoryQueue &q = queues.front();
char cmd[256];
sprintf(cmd, "svnadmin create /home/svn/%s/%s/%s", q.GetPublicStatus().c_str(),
q.GetUsername().c_str(), q.GetRepositoryName().c_str());
if(this->DeleteQueuedRepository(q.GetQueueId()))
{
printf("query deleted?\n");
}
printf("Repository created!\n");
queues.pop();
}
}
boost::this_thread::sleep(boost::posix_time::milliseconds(500));
//}
}
protected:
/**
* Gets the latest queue of repositories from the database
* and returns them inside a cool queue defined with the
* RepositoryQueue class.
*/
std::queue<RepositoryQueue> GetQueue()
{
std::queue<RepositoryQueue> queues;
Query query = this->_con.query("CALL sp_GetRepositoryQueue();");
StoreQueryResult result = query.store();
RepositoryQueue rQ;
if(result.num_rows() > 0)
{
for(unsigned int i = 0;i < result.num_rows(); ++i)
{
rQ = RepositoryQueue((unsigned int)result[i][0],
(unsigned int)result[i][1],
(String)result[i][2],
(String)result[i][3],
(String)result[i][4],
(bool)result[i][5]);
queues.push(rQ);
}
}
return queues;
}
/**
* Allows the thread to be shut off.
*/
void ChangeRunningState(bool isRunning)
{
this->_isRunning = isRunning;
}
/**
* Returns the running value of the active thread.
*/
bool IsRunning()
{
return this->_isRunning;
}
/**
* Deletes the repository from the mysql queue table. This is
* only called once it has been created.
*/
bool DeleteQueuedRepository(unsigned int id)
{
char cmd[256];
sprintf(cmd, "DELETE FROM RepositoryQueue WHERE Id = %d LIMIT 1;", id);
Query query = this->_con.query(cmd);
return (query.exec());
}
};
I've removed all the other methods as they're not needed...
Basically it's the DeleteQueuedRepository method which isn't working, the GetQueue works fine.
PS: This is on a Linux OS (Ubuntu server)
Many thanks,
Shaun

MySQL++ doesn't have a free_result method... or does it?
It doesn't need one. When the result object goes out of scope at the end of GetQueue(), all memory associated with it is automatically freed.
this->_con = Connection(false);
Three problems here:
When you create the RepositoryChecker object, you already have created a Connection object. If you need to pass different parameters to its constructor, you'd do that in the initialization list of the RepositoryChecker constructor, not in its body. Read your C++ book.
What you've done here instead is a) create a default Connection object, then b) create a different Connection object with exceptions turned off, then c) overwrite the first with the second. If that works, it's highly inefficient. MySQL++ Connection objects have had problems with their copy ctors in the past, so if you're using an old version of the library, it could explain your problems.
You're telling the Connection object (and every object it creates, even indirectly, which means pretty much everything in MySQL++) you don't want it to throw exceptions, but then you wrap it in a big try block. Pick one.
I'd suggest using exceptions — the default in MySQL++ — given the way your code is currently structured. If there is a query error way down in DeleteQueuedRepository(), there's no way to see what happened because you'd just pass false up to the caller, which is ignored because there is no else clause on the call. If you do this, log the e.what() message in your catch block. You're just throwing that information away right now.
There are several places where you're using constructs that look more like Python (or perhaps JavaScript) than C++. This makes me wonder if your problem isn't damage caused by some other misuse of C++.
On this line in particular, you're using the this pointer explicitly, for which there is no need in C++. This code does exactly the same thing:
_con = Connection(false);
Though again, the line should be replaced entirely, using the RepositoryChecker ctor initializer list instead.
Moving on...
sprintf(cmd, "DELETE FROM RepositoryQueue WHERE Id = %d LIMIT 1;", id);
As others have commented, you'd be better off using the Query stream interface:
Query q = _con.query();
q << "DELETE FROM RepositoryQueue WHERE Id = " << id << " LIMIT 1";
This has several advantages:
Fixes the type safety problem implied by the one who suggested changing your %d to %u. C++ IOStreams take care of that for you.
Automatic quoting of data inserted into the stream, if needed. (Which it isn't, in this case.)
Prevents any possibility of running off the end of the buffer. You could use the nonportable snprintf() instead here, but why?
If you're really happy with printf(), there's the template query interface instead.
boost::this_thread::sleep(boost::posix_time::milliseconds(500));
Have you read the threads chapter in the user manual? You don't get thread safety for free in MySQL++. Your problem could be due to memory corruption.
Warren Young, MySQL++ Maintainer

Try changing "%d" to "%u" in sprintf.

Related

how to correctly pass data structures between custom llvm passes

I have a Function pass, called firstPass, which does some analysis and populates:
A a;
where
typedef std::map< std::string, B* > A;
class firstPass : public FunctionPass {
A a;
}
typedef std::vector< C* > D;
class B {
D d;
}
class C {
// some class packing information about basic blocks;
}
Hence I have a map of vectors traversed by std::string.
I wrote associated destructors for these classes. This pass works successfully on its own.
I have another Function pass, called secondPass, needing this structure of type A to make some transformations. I used
bool secondPass::doInitialization(Module &M) {
errs() << "now running secondPass\n";
a = getAnalysis<firstPass>().getA();
return false;
}
void secondPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<firstPass>();
AU.setPreservesAll();
}
The whole code compiles fine, but I get a segmentation fault when printing this structure at the end of my first pass only if I call my second pass (since B* is null).
To be clear:
opt -load ./libCustomLLVMPasses.so -passA < someCode.bc
prints in doFinalization() and exits successfully
opt -load ./libCustomLLVMPasses.so -passA -passB < someCode.bc
gives a segmentation fault.
How should I wrap this data structure and pass it to the second pass without issues? I tried std::unique_ptr instead of raw ones but I couldn't make it work. I'm not sure if this is the correct approach anyway, so any help will be appreciated.
EDIT:
I solved the problem of seg. fault. It was basically me calling getAnalysis in doInitialization(). I wrote a ModulePass to combine my firstPass and secondPass whose runOnModule is shown below.
bool MPass::runOnModule(Module &M) {
for(Function& F : M) {
errs() << "F: " << F.getName() << "\n";
if(!F.getName().equals("main") && !F.isDeclaration())
getAnalysis<firstPass>(F);
}
StringRef main = StringRef("main");
A& a = getAnalysis<firstPass>(*(M.getFunction(main))).getA();
return false;
}
This also gave me to control the order of the functions processed.
Now I can get the output of a pass but cannot use it as an input to another pass. I think this shows that the passes in llvm are self-contained.
I'm not going to comment on the quality of the data structures based on their C++ merit (it's hard to comment on that just by this minimal example).
Moreover, I wouldn't use the doInitialization method, if the actual initialization is that simple, but this is a side comment too. (The doc does not mention anything explicitly about it, but if it is ran once per Module while the runOn method is ran on every Function of that module, it might be an issue).
I suspect that the main issue seems to stem from the fact A a in your firstPass is bound to the lifetime of the pass object, which is over once the pass is done. The simplest change would be to allocate that object on the heap (e.g. new) and return a pointer to it when calling getAnalysis<firstPass>().getA();.
Please note that using this approach might require manual cleanup if you decide to use a raw pointer.

Using an object by calling class constructor explicitly vs by default initialization + assignment operator

Considering the following example:
#include <wx/bitmap.h>
int main()
{
wxBMPHandler h;
wxImage::AddHandler(&h);
wxBitmap bm = wxBitmap(200, 200);
bm.SaveFile("file.bmp", wxBITMAP_TYPE_BMP);
return 0;
}
Since I'm only using h to call AddHandler() and not for anything else, I'd like to avoid defining it altogether and do the whole thing in one line. So I thought about replacing that with:
wxImage::AddHandler(&wxBMPHandler());
which compiles fine, but calling SaveFile() won't work then; WxWidgets will present an error stating "No image handler for type 1 defined" at runtime.
I guess the object created inside the function call is temporary, but I'm not sure about that. If not, what am I missing, and how can I avoid defining h?
It's worth noting that AddHandler() has the following signature:
static void AddHandler( wxImageHandler *handler );
[Update]
In response to M.M's comment saying:
wxImage::AddHandler(&wxBMPHandler()); should fail to compile, unless
that class has overloaded operator& for rvalues
Since I couldn't find a definition for operator& in WxWidgets' source code, I created this test project:
#include <iostream>
#include <string>
using namespace std;
string* address = nullptr;
void testing(string* input)
{
*input = "Something else entirely";
address = input;
}
int main()
{
testing(&string("Life is a test"));
cout << *address << endl;
cin.get();
return 0;
}
It compiles fine, and runs without any "hard error" - the only caveat is that nothing is shown in the screen - (*address).empty() returns true.
I even defined my own class to test with, instead of std::string and yielded the same behavior (no compiler error, no runtime error, but no output).
I also tried this one-liner, as suggested by aichao, without success:
wxImage::AddHandler(shared_ptr<wxBMPHandler>(new wxBMPHandler()).get());
I've never used wxWidgets before, but according to the wxWidgets version 3.1.1 API docs here, you should call wxImage::AddHandler using a heap-allocated handler object:
wxImage::AddHandler(new wxBMPHandler);
Therefore, there is no need for defining h. Also according to the docs, the memory for this handler object is managed by the wxWidgets framework. Specifically, the docs says that the handler is a
heap-allocated handler object which will be deleted by wxImage if it is removed later by RemoveHandler() or at program shutdown.
There is also the static member function wxImage::CleanUpHandlers() to delete all registered image handlers. According to the docs:
This function is called by wxWidgets on exit.
Therefore, you do not have to delete the handler yourself unless you specifically want to (i.e., to free up some memory).
Hope this helps.
In wxImage::AddHandler(&wxBMPHandler());, the lifetime of the temporary stop at the end of the expression, so you have dangling pointer.
In
wxBMPHandler h;
wxImage::AddHandler(&h);
wxBitmap bm = wxBitmap(200, 200);
bm.SaveFile("file.bmp", wxBITMAP_TYPE_BMP);
h outlives the call bm.SaveFile("file.bmp", wxBITMAP_TYPE_BMP);.
You will have similar issue with
{
wxBMPHandler h;
wxImage::AddHandler(&h);
} // End of life time of h
wxBitmap bm = wxBitmap(200, 200);
bm.SaveFile("file.bmp", wxBITMAP_TYPE_BMP);

Access violation on std::function assignement using lambdas

Hy everyone, here again. Continuing the code from my previous question : Is this a bad hack? memcpy with virtual classes
I corrected that, using the Clone approach as suggested, but I'm having an error that also happened before I tried the memcpy thing(read question above).
What I'm trying to do is to create a lambda that captures the current script and executes it, and then pass and store that lambda in an object ( Trigger*), in the member InternalCallback.
I get an access violation error on the lambda assignment: http://imgur.com/OKLMJpa
The error happens only at the 4th iteration of this code:
if(CheckHR(EnginePTR->iPhysics->CreateFromFile(physicsPath,StartingTriggerID,trans,scale,-1,false,engPtr)) == HR_Correct)
{
_Lua::ScriptedEntity * newScript = EntityBase->Clone(vm);//nullptr;
string luaPath = transforms.next_sibling().next_sibling().first_attribute().as_string();
if(UseRelativePaths)
{
stringstream temp2;
temp2 << _Core::ExePath() << LuaSubfolder << "\\" << luaPath;
luaPath = temp2.str();
}
newScript->CompileFile(luaPath.c_str());
newScript->EnginePTR_voidptr = engPtr;
auto callback = [=](_Physics::Trigger* trigger,PxTriggerPair* pairs, PxU32 count)
{
newScript->SelectScriptFunction("TriggerCallback");
newScript->AddParam(trigger->Id);
auto data = (_Physics::RayCastingStats*)pairs->otherShape->userData;
newScript->AddParam((PxU8)pairs->flags);
newScript->AddParam(data->ID);
newScript->AddParam((int)data->Type);
newScript->AddParam((int)count);
newScript->Go(1);
return;
};
((_Physics::Trigger*)EnginePTR->iPhysics->GetPhysicObject(StartingTriggerID))->InternalCallback = callback;
StartingTriggerID++;
}
This is the code for Trigger
class Trigger : public PhysicObject
{
public:
Trigger()
{
ActorDynamic = nullptr;
ActorStatic = nullptr;
InternalCallback = nullptr;
}
virtual HRESULT Update(float ElapsedTime,void * EnginePTR);
virtual HRESULT Cleanup(); // Release the actor!!
long Id;
ShapeTypes Type;
static const PhysicObjectType PhysicsType = PhysicObjectType::Trigger;
PxVec3 Scale;
void* UserData;
void Callback(PxTriggerPair* pairs,PxU32 count)
{
InternalCallback(this,pairs,count);
}
function<void(_Physics::Trigger* trigger,PxTriggerPair* pairs, PxU32 count)> InternalCallback;
};
By iteration I mean that is part of a for loop.
My system is Win 7 64 bits, Intel i3, NVIDIA GTX 480, and the compiler Visual Studio 2012 Express, using the C++11 toolset.
I'm really out of ideas. I tested for heap corruption, it appears to be good, I changed the capture in the lambda, changed nothing, I skip the 4th object and it works.
Any help would be really appreciated.
Edit: As required, here is the callstack: http://imgur.com/P7P3t4k
Solved. It was a design error. I store a lot of objects in a map, and they all derive from an object class ( like above, where Trigger derives from PhysicObject ).
The problem was that I was having IDs collisions, so the object stored in ID 5 wasn't a Trigger, so the cast created a bad object, and so the program crashed.
Silly error, really specific, but it might help somebody to remember to check temporal objects.

Error apparently raised by not yet executed code

I'm learning c++ by writing a program to convert MIDI files to Lilypond source files.
My program is composed by two main parts:
a MIDI file parser, that creates an object called MidiFile.
a converter that takes a MidiFile objects and converts it to a Lilypond source.
Today I've started coding the converter, and while I was testing it a strange error occurred: the program dies after an exception being thrown, more specifically a HeaderError, that means that the header chunk in the MIDI file is not as expected. It wouldn't seem that strange, but this error shows up only if I add a line of code after the buggy code! I add the main() function to better explain myself
#include <iostream>
#include "midiToLyConverter.hpp"
int main(){
// a queue to store notes that have not yet been shut down
using MidiToLyConverter::Converter::NoteQueue;
// representation of a note
using MidiToLyConverter::Converter::Note;
// the converter class
using MidiToLyConverter::Converter::Converter;
// the midifile class
using Midi::MidiFile;
// representation of a midi track
using Midi::MidiTrack;
// representation of a midi event
using Midi::MidiEvents::Event;
Parser::Parser parser = Parser::Parser(); // parser class
parser.buildMidiFile(); // builds the midi file from a .mid
Midi::MidiFile* midiFile = parser.getMidiFile(); // gets the MidiFile object
// iterates over all the tracks in the MidiFile
while(midiFile->hasNext()){
std::cout<< "==========\n";
MidiTrack* track = midiFile->nextTrack();
// iterates over all events in a track
while(track->hasNext()){
Event* event = track->nextEvent();
if (event->getEventType() == Midi::MidiEvents::NOTE_ON ||
event->getEventType() == Midi::MidiEvents::NOTE_OFF
)
// print the event if it's a note on or off
event->print();
}
}
return 0;
}
With my main() like this, everything works properly, but, if I add something between buildMidiFile and the while loop, the function buildMidiFile throws the exception!!!
Even if it's a completely unrelated instruction!
#include <iostream>
#include "midiToLyConverter.hpp"
int main(){
using MidiToLyConverter::Converter::NoteQueue;
using MidiToLyConverter::Converter::Note;
using MidiToLyConverter::Converter::Converter;
using Midi::MidiFile;
using Midi::MidiTrack;
using Midi::MidiEvents::Event;
Parser::Parser parser = Parser::Parser(); // parser class
parser.buildMidiFile(); // THE EXCEPTION IS THROWN HERE
Midi::MidiFile* midiFile = parser.getMidiFile(); // gets the MidiFile object
// adding this causes the exception to be thrown by the function
// buildMidiFile() called 5 lines above!
std::vector<bool>* vec = new std::vector<bool>();
// iterates over all the tracks in the MidiFile
while(midiFile->hasNext()){
std::cout<< "==========\n";
MidiTrack* track = midiFile->nextTrack();
// iterates over all events in a track
while(track->hasNext()){
Event* event = track->nextEvent();
if (event->getEventType() == Midi::MidiEvents::NOTE_ON ||
event->getEventType() == Midi::MidiEvents::NOTE_OFF
)
// print the event if it's a note on or off
event->print();
}
}
return 0;
}
I can't explain myself how this is possible. So if anyone has ideas or advices, all the help would be greatly appreciated :) If it's helpful I can post the source code for other classes and/or functions.
Solved! As pointed out in comments to the question, it was a problem caused by some sort of memory corruption. As suggested I used a memory checher (valgrind) and found out that it was a really stupid error: i simply forgot to initialize a variable in a for loop, something like
for (int i; i < limit ; i++)
and this led to that strange error :-) Initializing i to 0 solved the problem, and now the program works with Parser object placed either on the stack or on the heap.
So I suggest others incurring in similar problems to use a memory checker to control the memory usage of their program. Using valgrind is really simple:
valgrind --leak-check=yes yourProgram arg1 arg2
where arg1 and arg2 are the (eventual) arguments that your program requires.
Furthermore compiling your program with the -g flag (at least on g++, I don't know on other compilers), valgrind will also tell you at wich line of code the memory leak occurred.
Thanks to everybody for the help!
Regards
Matteo

How to serialize an object to send over network

I'm trying to serialize objects to send over network through a socket using only STL. I'm not finding a way to keep objects' structure to be deserialized in the other host. I tried converting to string, to char* and I've spent a long time searching for tutorials on the internet and until now I have found nothing.
Is there a way to do it only with STL?
Are there any good tutorials?
I am almost trying boost, but if there is how to do it with STL I'd like to learn.
You can serialize with anything. All serialization means is that you are converting the object to bytes so that you can send it over a stream (like an std::ostream) and read it with another (like an std::istream). Just override operator <<(std::ostream&, const T&) and operator >>(std::istream&, T&) where T is each of your types. And all the types contained in your types.
However, you should probably just use an already-existing library (Boost is pretty nice). There are tons of things that a library like Boost does for you, like byte-ordering, taking care of common objects (like arrays and all the stuff from the standard library), providing a consistent means of performing serialization and tons of other stuff.
My first question will be: do you want serialization or messaging ?
It might seem stupid at first, since you asked for serialization, but then I have always distinguished the two terms.
Serialization is about taking a snapshot of your memory and restoring it later on. Each object is represented as a separate entity (though they might be composed)
Messaging is about sending information from one point to another. The message usually has its own grammar and may not reflect the organization of your Business Model.
Too often I've seen people using Serialization where Messaging should have been used. It does not mean that Serialization is useless, but it does mean that you should think ahead of times. It's quite difficult to alter the BOM once you have decided to serialize it, especially if you decide to relocate some part of information (move it from one object to another)... because how then are you going to decode the "old" serialized version ?
Now that that's been cleared up...
... I will recommend Google's Protocol Buffer.
You could perfectly rewrite your own using the STL, but you would end up doing work that has already been done, and unless you wish to learn from it, it's quite pointless.
One great thing about protobuf is that it's language agnostic in a way: ie you can generate the encoder/decoder of a given message for C++, Java or Python. The use of Python is nice for message injection (testing) or message decoding (to check the output of a logged message). It's not something that would come easy were you to use the STL.
Serializing C++ Objects over a Network Socket
This is 6 years late but I just recently had this problem and this was one of the threads that I came across in my search on how to serialize object through a network socket in C++. This solution uses just 2 or 3 lines of code. There are a lot of answers that I found work but the easiest that I found was to use reinterpret_cast<obj*>(target) to convert the class or structure into an array of characters and feed it through the socket. Here's an example.
Class to be serialized:
/* myclass.h */
#ifndef MYCLASS_H
#define MYCLASS_H
class MyClass
{
public:
int A;
int B;
MyClass(){A=1;B=2;}
~MyClass(){}
};
#endif
Server Program:
/* server.cpp */
#include "myclass.h"
int main (int argc, char** argv)
{
// Open socket connection.
// ...
// Loop continuously until terminated.
while(1)
{
// Read serialized data from socket.
char buf[sizeof(MyClass)];
read(newsockfd,buf, sizeof(MyClass));
MyClass *msg = reinterpret_cast<MyClass*>(buf);
std::cout << "A = " << std::to_string(msg->A) << std::endl;
std::cout << "B = " << std::to_string(msg->B) << std::endl;
}
// Close socket connection.
// ...
return 0;
}
Client Program:
/* client.cpp */
#include "myClass.h"
int main(int argc, char *argv[])
{
// Open socket connection.
// ...
while(1)
{
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
MyClass msg;
msg.A = 1;
msg.B = 2;
// Write serialized data to socket.
char* tmp = reinterpret_cast<char*>(&msg);
write(sockfd,tmp, sizeof(MyClass));
}
// Close socket connection.
// ...
return 0;
}
Compile both server.cpp and client.cpp using g++ with -std=c++11 as an option. You can then open two terminals and run both programs, however, start the server program before the client so that it has something to connect to.
Hope this helps.
I got it!
I used strinstream to serialize objects and I sent it as a message using the stringstream's method str() and so string's c_str().
Look.
class Object {
public:
int a;
string b;
void methodSample1 ();
void methosSample2 ();
friend ostream& operator<< (ostream& out, Object& object) {
out << object.a << " " << object.b; //The space (" ") is necessari for separete elements
return out;
}
friend istream& operator>> (istream& in, Object& object) {
in >> object.a;
in >> object.b;
return in;
}
};
/* Server side */
int main () {
Object o;
stringstream ss;
o.a = 1;
o.b = 2;
ss << o; //serialize
write (socket, ss.str().c_str(), 20); //send - the buffer size must be adjusted, it's a sample
}
/* Client side */
int main () {
Object o2;
stringstream ss2;
char buffer[20];
string temp;
read (socket, buffer, 20); //receive
temp.assign(buffer);
ss << temp;
ss >> o2; //unserialize
}
I'm not sure if is necessary convert to string before to serialize (ss << o), maybe is possible directly from char.
I think you should use google Protocol Buffers in your project.In network transport Protocol buffers have many advantages over XML for serializing structured data. Protocol buffers:
are simpler
are 3 to 10 times smaller
are 20 to 100 times faster
are less ambiguous
generate data access classes that are easier to use programmaticall
and so on. I think you need read https://developers.google.com/protocol-buffers/docs/overview about protobuf